In that case it is easy. Where the original ballast is, connect all wires together. Use the original coil+ wire to feed power to your new ignition
You should have:
IGN1 coming out of the bulkhead, usually dark blue
IGN2 coming out of the bulkhead, usually brown
The wire going from ballast to coil+ usually dark blue
The wire going from ballast to voltage regulator usually dark blue
If it was previously converted to electronic, I'd just carefully strip all that out